How do i determine the exact equation of a parabola (in standard form [ax2^ + bc + c]) from a graph

X=1, it crosses y at 3, and it is a negative parabola.
Using guess and check, (also knowing c must be 3, a must be negative and half of b, and knowing x is 1), I got y=(-x^2)+(2x)+(3). After graphing this, it was the correct parabola.

The answer would be c.hope this .